In order to manufacture a highly integrated semiconductor device, first of all, a conductive thin film such as a metal film, etc. which will serve as a wiring material for conduction or an interlayer insulation film for the purpose of insulating conductive thin films from each other is formed on a device such as a silicon wafer, etc. Thereafter, a  photoresist is uniformly coated on the surface of this conductive thin film or interlayer insulation film to provide a photosensitive layer, to which is then applied selective exposure and development treatments to prepare a desired resist pattern. Subsequently, a dry etching treatment is applied to the interlayer insulation film while using this resist pattern as a mask, thereby forming a desired pattern on the subject thin film. Then, there is generally adopted a series of steps of completely removing the resist pattern and a residue generated due to the dry etching treatment by means of ashing with oxygen plasma, etc. or using a prescribed cleaning liquid.
In recent years, miniaturization of a design rule advances so that signal transmission delay dominates the limits of high-speed arithmetic processing. For that reason, transition from aluminum to copper with lower electrical resistance as the wiring material for conduction is advancing. Also, transition from a silicon oxide film to a low dielectric interlayer insulation film having a dielectric constant of lower than 3 (hereinafter sometimes referred to as “Low-k film”) as the interlayer insulation film is advancing. For example, an organosiloxane thin film containing a light absorbing compound (hereinafter referred to as “organosiloxane-based thin film”) having (1) a function to  fill in gaps such as projections and recesses, grooves, etc. of a base element to achieve flattening, (2) a function to absorb radiations reflected from the device or (3) a function to keep the shape of the interlayer insulation film at the time of dry etching to make it easy to achieve precise microfabrication has been provided between the photoresist and the interlayer insulation film.
However, in the case of removing the photoresist or the organosiloxane-based thin film by means of ashing, there is a concern that the Low-k film existing beneath the organosiloxane-based thin film is exposed to oxygen plasma or the like and damaged. For example, in the pattern formation by a via-first dual damascene process, in removing the organosiloxane-based thin film filled in a via part, the Low-k film in the surroundings of the via part is damaged. As a result, there is caused a problem that an electric characteristic is conspicuously deteriorated. Accordingly, in manufacturing a semiconductor device in which the Low-k film is used, there is demanded a method of exhibiting photoresist removal properties to the same extent as that in an oxygen plasma ashing step while suppressing the damage of the subject Low-k film and capable of removing the photoresist by other means than ashing. 
As a method for solving these problems, there are proposed methods of pre-treating with a hydrogen peroxide-containing cleaning liquid and treating with an amine-based stripping liquid (see Japanese Patent No. 3516446, JP-A-2003-140364 and JP-A-2006-106616). However, these treatment methods are a two-stage process, and more simplification of the process is desired. For that reason, there is proposed, as a cleaning liquid, an oxidizing agent-containing cleaning liquid capable of removing a residue generated by a dry etching treatment (hereinafter sometimes referred to as “etching residue”), a modified photoresist in which a surface layer part of a photoresist layer has been modified by the dry etching treatment and an unmodified photoresist layer located in a lower layer than the subject modified photoresist by a one-stage process.
Specifically, there are proposed oxidizing agent aqueous solutions such as hydrogen peroxide, ozone water, etc., or cleaning liquids obtained by adding a basic water-soluble fluoride, an amine, quaternary ammonium hydroxide, an acid, a chelating agent, a water-soluble fluorine compound, a quaternary ammonium salt, a surfactant, a solvent or the like to such an oxidizing agent aqueous solution (see JP-A-10-298589, JP-A-2000-56478, JP-A-2000-258924, JP-A-2002-202617, JP-A-2003-5383, JP-A-2003-124173, JP-A-2003-221600 and JP-A-2004-4775).
However, even in the case of using the foregoing cleaning liquid, there are involved such problems that it is difficult to remove the organosiloxane-based thin film and the etching residue as well as the modified photoresist and the unmodified photoresist layer without damaging the copper wiring and the Low-k film and so on and that the use for a long time or the storage over a long period of term is difficult.
Furthermore, the foregoing patent documents neither describe nor suggest a cleaning liquid which is suitable for flattening and the dual damascene process using an antireflection film or a thin film for precise microfabrication (for example, an organosiloxane-based thin film) and a cleaning method thereof.
As a cleaning liquid capable of removing the modified photoresist and the unmodified photoresist layer, JP-A-2004-212818 proposes a cleaning liquid having a pH of 5 or more and containing hydrogen peroxide and an alkali metal ion. However, even the subject patent document neither describes nor suggests a cleaning liquid which is suitable for the dual damascene process using an organosiloxane-based thin film and a cleaning method thereof. 